A conventional scanning exposure apparatus forms and projects the image of a pattern of an original (reticle or photomask) onto a substrate (wafer) through a projection optical system, and scans (moves) the original and substrate simultaneously with respect to the projection optical system.
FIG. 3 is a perspective view showing the schematic arrangement of the conventional scanning exposure apparatus. FIG. 4 is a front view showing the schematic arrangement of the conventional scanning exposure apparatus.
An original 1 (reticle) is held by an original stage 2 which is driven in a Y direction in FIG. 3 by a laser interferometer 3 and a drive control means (not shown).
In the vicinity of the original 1, reference originals 4a and 4b are fixed within a predetermined range of the original stage 2. The reflection surfaces of the reference originals 4a and 4b are almost flush with the reflection surface of the original 1. A plurality of original reference marks made of a metal such as Cr or Al are formed on the reflection surfaces of the reference originals 4a and 4b serving as reference portions.
The original stage 2 is driven while its position in a Z direction in FIG. 3 is held constant with respect to a projection optical system 5. A moving mirror 6 which reflects a beam emitted from the laser interferometer 3 is fixed to the original stage 2. The laser interferometer 3 measures the position and moving amount of the original stage 2 successively.
A predetermined pattern formed on the original 1 is illuminated by exposure light emitted from an illumination optical system 7, and is projected through the projection optical system 5 to form an image on a substrate 8 (wafer) held by a substrate stage 9.
In the vicinity of the substrate 8, a reference substrate 10 is fixed within a predetermined range of the substrate stage 9. The reflection surface of the reference substrate 10 is almost flush with the upper surface of the substrate 8. A plurality of substrate reference marks made of a metal such as Cr or Al are formed on the reflection surface of the reference substrate 10.
The substrate stage 9 has a drive control means (not shown) for rotatably driving the substrate 8 or reference substrate 10 during vertical driving, image surface blur correction driving, alignment and yawing control of the substrate 8 or reference substrate 10, so that the substrate 8 coincides with the image surface of the projection optical system. Furthermore, a moving mirror 12 which reflects a beam from a laser interferometer 11 is fixed to the substrate stage 9. The laser interferometer 11 measures the position and moving amount of the substrate stage 9 successively.
With the above arrangement, the substrate stage 9 can move in the direction of the optical axis (Z direction) of the projection optical system 5 and within a plane (X-Y plane.) perpendicular to the direction of the optical axis, and can be rotated (θ direction) about the optical axis.
The original 1 and substrate 8 are placed at optically conjugate positions through the projection optical system 5 by a plurality of position detection means. The illumination optical system 7 forms a slit-like exposure region or arcuate exposure region elongated in the X direction on the original 1. The exposure region on the original 1 forms a slit-like exposure region, having a size substantially proportional to the projection magnification of the projection optical system 5, on the substrate 8.
In the above scanning exposure apparatus, both the original stage 2 and substrate stage 9 are driven with respect to the optical path of the exposure light at a speed ratio corresponding to the optical magnification of the projection optical system 5, to scan the exposure region on the original 1 and that on the substrate 8, thus performing scanning exposure.
An oblique incident scheme first position detection means 13 is provided as a focal plane position detection means. The first position detection means 13 irradiates the surface of the substrate 8 (or the surface of the reference substrate 10), where the pattern of the original 1 is to be transferred by the projection optical system 5, in an oblique direction with non-exposure light, and detects light reflected obliquely by the surface of the substrate 8 (or the surface of the reference substrate 10).
A plurality of position detection light-receiving elements corresponding to the respective reflected beams are provided to the first position detection means 13, and are arranged such that the light-receiving surfaces of the respective position detection light-receiving elements and the reflection points of the respective beams on the substrate 8 are substantially conjugate. Therefore, a positional error of the substrate 8 (or reference substrate 10) depending on the direction of the optical axis of the projection optical system 5 is measured as a positional error of the corresponding position detection light-receiving element in a detection unit.
When, however, the projection optical system 5 absorbs exposure heat or the ambient atmosphere changes, the focal position of the projection optical system 5 changes, and an error occurs in the measurement origin and focal plane of the oblique incident scheme first position detection means 13. A second position detection means 14 is loaded to calibrate this error.
As shown in FIG. 3, the second position detection means 14 has a first position detection system 14a and second position detection system 14b as two position detection systems. The two position detection systems 14a and 14b extract from the illumination optical system 7 light components having substantially the same wavelength as that of the exposure light, and guide them through fibers or lens optical systems. The guided light illuminates an in-focus mark on the reference original 4a or 4b (note that “a reference original 4” includes “the reference original 4a or 4b” unless otherwise specified).
At least one optical system in the second position detection means 14 is driven in the direction of the detection optical axis, and the detection focal plane of the second position detection means 14 is aligned with the in-focus mark on the reference original 4. Subsequently, the substrate stage 9 is vertically driven in the direction of the optical axis (Z direction) in the vicinity of the zero point which is preset by the oblique incident scheme first position detection means 13 in advance.
During driving, the reference substrate 10 is located substantially immediately under the projection optical system 5. Light transmitted through the in-focus mark of the reference original 4 is transmitted through the projection optical system 5 to irradiate the reference substrate 10. Light reflected by the reference substrate 10 is transmitted through the projection optical system 5 again to become incident on the light-receiving portion of the second position detection means 14 through the reference original 4.
The second position detection means 14 has detection ranges for the two position detection systems 14a and 14b on the X-axis including the optical path of the exposure light, as shown in FIG. 3, so that the means 14 estimates the actual exposure image surface from the two, left and right measurement points on the X-axis. The detection ranges of the first and second position detection systems 14a and 14b are arranged substantially symmetrically with respect to the optical path of the exposure light. The first and second position detection systems 14a and 14b are retracted so they do not shield the exposure light during exposure, and wait at retracted positions away from the exposure region.
The second position detection means 14 also serves as a position detection means which detects the positions of the reference original 4 and reference substrate 10 relative to each other. The detection results serve as elements for calculating the baselines of off-axis microscopes 15 and 16. A baseline is the distance between the center of a shot when aligning the substrate 8 and the center of a shot (optical axis of the projection optical system) for exposure. The off-axis microscope 15 is a non-TTL (Through The Lens) microscope which uses non-exposure light, and the off-axis microscope 16 is a TTL microscope which uses non-exposure light.
The off-axis microscopes 15 and 16 detect the position of an alignment mark on the substrate 8.
The detection scheme includes a scheme of illuminating the alignment mark with a laser beam or light emitted from a halogen lamp as a light source and having a wide wavelength band, and image-processing the image data of the sensed alignment mark, thus measuring the alignment mark, an interfering alignment scheme of irradiating a diffraction-grating-like alignment mark on the substrate with laser beams having the same frequency or slightly different frequencies in one or two directions, causing interference between the two diffracted light components, and measuring the position of the alignment mark from the phases of the two diffracted light components, and the like.
The outline of baseline measurement with the off-axis microscopes 15 and 16 in the conventional scanning exposure apparatus will be described.
According to baseline measurement of the conventional scanning exposure apparatus, the original stage 2 and substrate stage 9 are driven to predetermined positions, and the positions of the reference original 4 and reference substrate 10 relative to each other are detected by the second position detection means 14 (first step).
The reference substrate 10 is moved to the detection range of the off-axis microscope 15 or 16 by driving the substrate stage 9, and the position of the reference mark formed in the off-axis microscope 15 or 16 and the position of the reference mark on the reference substrate 10, which positions are relative to each other, are detected (second step).
The baseline of the off-axis microscope 15 or 16 is calculated from the detection results of the first and second steps, and the baseline of the off-axis microscope 15 or 16 is corrected with the calculation result (for example, see Japanese Patent Laid-Open Nos. 9-298147 and 10-79340).
Recently, the patterns of semiconductor integrated circuits are becoming largely integrated and shrinking in size more and more. To further improve the alignment accuracy and throughput of the entire apparatus, an increase in detection processing speed of various types of detection devices is required.
According to the prior art as described above, the two position detection systems 14a and 14b are mounted on the second position detection means 14 to perform measurement. This technique advances the limit for the recent technique of a larger integration degree and a smaller feature size.
During detection of the focal plane position using the second position detection means 14, as the actual exposure image surface is estimated from the two, left and right measurement values, the detection ranges of the two position detection systems 14a and 14b are formed coaxially on the right and left sides, as described above. Accordingly, with the conventional scanning exposure apparatus, baseline measurement and the like cannot be performed on the optical path of the exposure light, and may be adversely affected by distortion or the like caused by the aberration of the projection optical system.
In detection of the focal plane position, measurement must be performed as close as possible to the optical path of the exposure light. Hence, during exposure, the position detection system must be driven to retract from the exposure range. The detection time and detection accuracy may accordingly be adversely affected by driving.
With the conventional scanning exposure apparatus, since the two position detection systems 14a and 14b have the detection positions within the exposure slit, baseline measurement cannot be performed during exposure or at an exposure end position. Furthermore, in baseline measurement, the original stage 2 and substrate stage 9 must also be driven to predetermined baseline measurement positions. This poses an issue in the throughput of the entire apparatus.
As the patterns of the semiconductor integrated circuits or the like become largely integrated and shrink in size more and more, the NA of the projection optical system increases, and the outer shape of the projection optical system tends to become large. Accordingly, the non-TTL off-axis microscope provided in the vicinity of the projection optical system must be separated from the optical path of the exposure light. When the baseline becomes long in this manner, the baseline measurement accuracy decreases, and the alignment accuracy decreases.
As the wavelength of the exposure light becomes short, the transmittance of the exposure light with respect to an optical member decreases. Also, the exposure light quantity increases to improve the throughput of the entire apparatus. Therefore, the exposure light absorbed by the original increases, causing thermal deformation of the original. The conventional scanning exposure apparatus, however, does not have any position detection system that can detect the thermal deformation of the original during exposure.